The present invention relates generally to wireless communication systems and, in particular, to transmitting and receiving information in a time slot of a time division multiplexed wireless communication system.
Economics play an important role in the design of wireless communication systems. Bandwidth is limited and equipment is expensive, and therefore many schemes have been developed for multiplexing many different users over the same physical channel. One such scheme is time division multiple access (TDMA). In a TDMA system, the radio frequency (RF) signal carrying the information is segmented into intervals called time frames. Each frame is further partitioned into assignable user blocks of time called time slots. During each time slot, the assigned user of that slot is entitled to use the full spectrum of the RF signal. Each time slot within a frame might have a different user assigned to it, or one user might be assigned several time slots within a frame. The user of a communication unit, such as a mobile or portable radio or a cellular telephone, continues to occupy the same slot or slots in succeeding time frames until the user terminates his communication, is transferred to another base site, or is transferred to another sector within a base site.
During voice calls in a TDMA system, voice information is included in time slots in a discontinuous fashion. That is, voice information is not typically included in the time slots allocated to the user in every time frame because there are occasional lulls in voice activity when there is no voice information to be transmitted. However, leaving those time slots completely empty of information is undesirable. Providers of wireless communication services feel that a blank transmission during lulls in user activity would be discomforting for the recipient of the transmission, who might wonder as to whether the communication had been terminated. Therefore, background noise is transmitted during the lulls, which background noise indicates to the recipient a continuing connection to the user and a continuing active communication link. In addition, in the xe2x80x9ciDENxe2x80x9d system available from Motorola, Inc. of Schaumburg, Ill., system information is also transmitted during the lulls. The system information comprises information that allows the communication infrastructure to monitor the communication unit""s continuing presence, timing synchronization, and transmit signal quality. So, although there may not be any voice information to be conveyed, time slots transmitted during the voice activity lulls are nonetheless filled with background noise information and system information.
The drawback with respect to transmitting a completely filled time slot during the voice activity lulls is that the communication unit is transmitting information and consuming power, even though there is no voice information in the contents of the time slot (i.e., the contents of the time slot are of little value to the user of the communication unit). Since the power for operating the communication unit is a limited resource (i.e., the batteries providing the power have a limited life between recharges), minimization of the amount of power consumed by the communication unit in transmitting information during the lulls is a desirable goal. Battery size, rechargeable battery life, and the length of time of communication unit usage between each need to recharge the battery are visible areas of competition among manufacturers of communication units and improvements are constantly being sought that will extend battery life without increasing battery size.
Therefore, a need exists for a method and apparatus for transmitting and receiving information in a time slot at a reduced level of power consumption by the transmitting communication device.